WASHINGTON — The risk of an unprecedented evacuation of the International Space Station will spike if Russian craft cannot resume their missions and return by November, a senior NASA official has warned.
"There is a greater risk of losing the ISS when it's unmanned than if it were manned," Michael Suffredini, the ISS program manager for the US space agency, said in a conference call with Russian officials.
"The risk increase is not insignificant," he added.
Russia on Monday delayed its next manned mission to the ISS by at least a month after an unmanned cargo vessel crashed into Siberia instead of reaching orbit on August 24. The head of Russia's manned spaceflight programme also warned that a significantly longer delay would force the six people on board the station to abandon the orbiter due to fatigue and supply problems.
The station crew normally consists of six -- currently three Russians, two Americans and one Japanese -- working six-month rotations.
Staff safety and the "very big investment" that the Russian and US governments have made in the ISS would guide future decisions, Suffredini said during the call on Monday.
"We prefer not to operate in that condition without crew on board for an extended period of time just to make sure we end up in that situation.
"But assuming the systems keep operating we can command the station from the ground and operate it on orbit indefinitely," Suffredini added.
The ISS, which orbits 350 kilometers (220 miles) above Earth, is a platform for scientific experiments bringing together space agencies from Russia, the United States, Europe, Japan, and Canada.
Launched in 1998, it was initially expected to remain in space for 15 years until an agreement was reached to keep it operating through 2020.
An evacuation of the ISS was planned after the Columbia shuttle disaster which killed seven astronauts in 2003, but NASA later decided to keep staff on board the station at all times.
Russian officials expect the next manned launch of its Soyuz craft to take place in late October or early November -- it had initially been scheduled for September 22.
A crew comprising Russians Andrei Borisenko and Alexander Samokutyaev and NASA astronaut Ron Garan went up to the ISS in March to honor the 50th anniversary of the first voyage of space pioneer Yuri Gagarin.
But this month's failed launch was a spectacular blow for Russia after it had become the sole nation capable of taking humans to the ISS after the July withdrawal of the US space shuttle.